12v battery dies on the 405

Any time the Prius is in Ready mode (eg if you can drive it, or if you've just shifted to Park), the engine will turn on as necessary to charge the traction battery, and the traction battery is always charging the 12V battery. You can actually run the car without the 12V battery installed at all; all the 12V systems are effectively powered by the DC-DC converter off the traction battery, whether the 12V battery is installed or not. In any case, starting the ICE is done from the traction battery, not the 12V battery; that's just used to boot the computers when you first turn on the car, or to run the radio and headlights if you're in ACC mode (or not in Ready mode), or things like that.

Can you describe more about how it died? Did the car turn off completely while you were driving? Were there any warning lights, or indications of power when you tried to turn it on? Were you in D at the time? Did you try turning it off and back on, or try to start it using the emergency start procedure (found somewhere deep in the manual)?

 

How new is it? It's possible there was a poorly connected cable that caused it to die. Probably won't happen again if that's the case.

As stated above, the 12V battery isn't used to "start the car". It's used to power the computers and other electronics so they can close a relay in the traction battery so -that battery- can be used to start the ICE, run the A/C, power the electric motors, etc.

If you're wondering why the car died and you still have headlamps and interior lights that aren't excessively dim, the 12V battery is not the problem.

Run out of gas?

 

Hi All,

As people have disconnected the 12 V battery, once started, and driven Gen II Prius around, I think this is something else than a discharged 12 V. Either its got a shorted cell, or there is another short/open in your 12 V system. Or at least - these are the first things to look for.

As DB attempted to clarify, the 12 V battery does not start the ICE. That is started by the traction battery sending electricity to the MG1 (about 7 hp motor in the transmission).

The 12 V battery just starts the computers that signal and control everything else. Another thing to check out is if one of these computers that went intermitant.

 

The bunch of Gen II's back in '04 & '05 had issues with the red triangel of death, where the ice would just die for no apparent reason. Toyota came up with a hardware flash that cured it. Ours didn't happen until the car was nearly 3 years old. Hope this isn't de ja vu for the Gen III. The only good thing about that early issue was that if you would simply wait for 10 to 20 minutes, the ecu's would reboot and you'd be good to go again ... until the next occurance.

.

 

I sat in stopped traffic for about 30 minutes while wreckers cleared cars off of the highway this summer and then stop-and-go for another 15 minutes in 95F heat with AC running. The HV battery dropped to 2 bars and the ICE would cycle on and charge back to 3 bars.

This continued for the entire time until I finally picked up enough speed for the ICE to run long enough to begin charging the HV battery above 3 bars. By the time I was back up to highway speed the HV was back to full charge.

I had no issues other than being a little worried about the HV battery dropping so low. So, this is not a Gen III issue but must be an issue with your 12V battery or system.

 

mmccarty,

At any time in that stop & go traffic were you in neutral while the radio and/or the A/C were on? In neutral the ICE won't start & neither of the batteries will charge. In that situation, if the 12V gets too low (due to the radio), then the HV battery which is supplying power to the 12V (through the inverter) will start running low & eventually when the HV battery gets too weak, the car will shut itself down to prevent any damage to the battery pack. As David Beale mentioned, how was your gas situation? Running out of gas will kill the car (& then you can't even limp to the side of the road on the electric motor like you could in the 2G).

Ken (in Bolton,Ct)

 

In the Gen II, there is no keep-charging/recharging the HV battery when
the car is in Neutral. Is this also true for the Gen III?

Any chance that you put the car in Neutral?

Could be an unconscious habit from your earlier, regular ICE-only car
days to reduce transmission friction losses while stopped in traffic.

This doesn't work on the Prius as there is no transmission per-se, and the
various bits in the drive train are "hooked up" at all times, Neutral just
being an electrical condition set by the HSD.

Edit: Ahh... "He who hesitates is lost." Ken, Nice post.

 

"12v Battery dies on the 405" -- Sounds like the title of a new horror movie.

Keith

 

Good to hear they are holding on to it - probably the worst thing Toyota wants to know about is a car that 'dies' while driving... I'm sure they will fix it, and not give it back until they have an idea of what really happened...